1. Field of the Invention
The present invention relates to a ceramic composition for a microwave dielectric (simply referred to as a dielectric ceramic composition), said microwave dielectric having a temperature coefficient of resonance frequency (simply referred to as .tau.f hereinafter) which is close to zero or has any controlled positive or negative value depending on the amount of ZnO added.
The microwave dielectric pertaining to the present invention will be used for microwave dielectric resonators, microwave IC substrates, and impedance matching in microwave circuits etc.
2. Description of the Prior Art
There are several known dielectric ceramic compositions which are represented by BaO.3.9-4.1TiO.sub.2 . xZnO (Japanese Patent Publication No. 37807/1989), BaO.4TiO.sub.2.x ZnO.yTa.sub.2 O.sub.5 (Japanese Patent Laid-open No. 10806/1986), BaO.4TiO.sub.2.x ZnO.yWO3 (Japanese Patent Laid-Open No. 10807/1986), and BaO.wTiO.sub.2.xBa(Zr.sub.1/3 Ta.sub.2/3)O.sub.3.yTa.sub.2 O.sub.5.zMnO.sub.2 (Japanese Patent Laid-open No. 117957/1988).
Of the above-mentioned four dielectric ceramic compositions, the first three vary in .tau.f (which ranges from positive to negative) depending on the amount of additives. However, they are often poor in sinterability, and there has been a demand for a new dielectric ceramic composition of different make-up which is comparable or superior to the conventional ones in performance. And the last one does not have negative .tau.f values.